Oxo complexes of rhenium

Again, fluoro and oxo complexes of rhenium predominate. The reaction of KF and ReFe in an inert PTFE vessel yields pink K2[ReFs], the anion of which has a square-prismatic structure hydrolysis converts it to K[ReOFs]. 

In the bifunctional radiopharmaceuticals, Tc and Re complexes that are suitable for coupling to antibodies are almost square-pyramidal oxo complexes of tetradentate ligands, as mentioned earlier. Spies et al. [65] recently studied the syntheses and structures of rhenium complexes with a tetradentate NS3 tripod ligand 2, 2,, 2"-nitrilotris(ethanethiol) (l in Fig. 9) as an interesting alternative to the oxo complex. Such ligands could lead to weakly polar, trigonal-bipyramidal complexes in which the metal atom is more strongly shielded than in the square-pyramidal oxo complexes. Schemes for the syntheses... 

Several oxo-bridged mixed fluoro-hydroxo-oxalato complexes of rhenium(V) that are prepared by boiling freshly precipitated Re02 with oxalic acid and 40% HF may actually be derivatives of the [Re203]4+ moiety. They have been formulated as containing the [Re20(C204)(0H)6F2]2- anion but remain inadequately characterized.396... 

On the other hand a coordinatively unsaturated paramagnetic d metal center could oxidatively add the allyl radical at the metal center to form a labile d° n-aWyl oxo species as organometallic intermediate (step B). The latter may rearrange via a ff-allyl intermediate to a d allyloxy species (step D). The latter is believed to convert to acrolein and a reduced metal center via an /0-hydrogen abstraction by the metal center. In an attempt to gain insight into fundamental reactions involved in this catalytic cycle, some authentic d° allyl 0X0 complexes of rhenium [23] and tungsten... 

Gable, Kevin P, Rhenium and Technetium Oxo Complexes in the Study of Organic... 

Scheme 17. Synthesis of mixed oxo-alkyi complexes of high valency technetium and rhenium...

Compounds and complexes of the early transition metals are oxophilic because the low d-electron count invites the stabilization of metal-oxo bonds by 7T-bond formation. To a substantial extent, their reactivity is typical of complexes of metals other than rhenium. That is particularly the case insofar as activation of hydrogen peroxide is concerned. Catalysis by d° metals - not only Revn, but also CrVI, WVI, MoVI, Vv, ZrIV and HfIV - has been noted. The parent forms of these compounds have at least one oxo group. Again the issue is the coordination of the oxygen donating substrate, HOOH, to the metal, usually by condensation ... 

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